The tools of 266 days were too expensive.
Bangladesh officially claim- 3 million Bengali were killed by Pakistan army & their auxiliary forces, at least 200 thousands women were victims of Genocidal rapes,10 million took refugees to India, 300 thousands internally displaced, unlimited property were damages, most of villages were burnt down, huge number of minorities were forcefully converted to Islam.
Genocidal Mass killing:
Although independent researchers, including the British Medical Journal, have put forward the figure ranging from between 125,000 and 505,000. American political scientist Rudolph Rummel puts total deaths at 1.5 million.
Whatever from Academic point of view, we know Number of casualties not the focus factor for a Genocide. The main issue is Intention to destroy. Pakistan Authority had been started oppression against Bengalis from 1947 and operation searchlight was the execution part of the Genocide to destroy the Bengali Nation.
According to the Asia Times, At a meeting of the military top brass, Yahya Khan declared: "Kill 3 million of them and the rest will eat out of our hands." Accordingly, on the night of 25 March, the Pakistani Army launched Operation Searchlight to "crush" Bengali resistance in which Bengali members of military services were disarmed and killed, students and the intelligentsia systematically liquidated and able-bodied Bengali males just picked up and gunned down.
The scale of the atrocities was first made clear in the West when Anthony Mascarenhas, a Pakistani journalist who had been sent to the province by the military authorities to write a story favorable to Pakistan's actions, instead fled to the United Kingdom and, on 13 June 1971, published an article in The Sunday Times describing the systematic killings by the military. The Heading of the article was “Genocide”.
Mascarenhas reported that he was repeatedly told by senior military officers in Dacca and comilla, ‘We are determined to cleanse East Pakistan once and for all of the threat of secession, even if it means killing off two million people and ruling the province as a colony for 30 years’. His evidence is of particular value, not only because he heard such remarks made by Pakistan officers when ‘off-guard’, but because he made contemporaneous records of the conversations in his diaries, many of which he smuggled out with him. Perhaps the most damning statement of all those he heard was one made by Major-General ShaukatRiza, commanding the 9th Division:
‘ You must be absolutely sure that we have not undertaken such a drastic and expensive operation- expensive both in men and money- for nothing. We have undertaken a job. We are going to finish it, not hand it over half done to the politicans so that they can messit up again. The army can’t keep coming back like this every three or four years. It has a important task. I assure you that when we have got through with what we are doing there will never be need again for such an operation’
Statements of this kind make clear that the atrocities committed against the population of East Pakistan were part of deliberate policy by a disciplined force. As such, they differ in character from the mob violence committed at times by Bengalis against Biharis. To quote Anthony Masacarenhas again (from a taped interview):
‘What struck me was the impression I got, a very hard impression, that this was a regular pattern. It wasn’t somebody venting his spleen, but he had clear orders to clean up. It was the pattern of the killing. You killed first Hindus, you killed every one of the East Pakistan Rifles, the Police, or the East Bengal Regiment you found, you killed the students, the male students, if you get a woman student you probably did something else, the teachers…the teachers are supposed to have been corrupted by the Hindus. It is the pattern that it most frightening. I have seen the partition riots in Delhi in 1947. That was mob frenzy. It was completely different here. This was organized killing, this is what terrifying about it. It was not being done by mobs. It was systematic organized thing.’ 
On 2 August 1971, Time magazine correspondent sent a dispatch that provided detailed description of the destruction in East Pakistan. It wrote that cities have whole sections damaged from shelling and aerial bombardments. The dispatch wrote: "In Dhaka, where soldiers set sections of the Old City ablaze with flamethrowers and then machine-gunned thousands as they tried to escape the cordon of fire, nearly 25 blocks have been bulldozed clear, leaving open areas set incongruously amid jam-packed slums." It quoted a senior US official as saying "It is the most incredible, calculated thing since the days of the Nazis in Poland."
Archer K. Blood, American diplomat wrote in the Blood Telegram: "with support of the Pak military, non-Bengali Muslims are systematically attacking poor people's quarters and murdering Bengalis and Hindus." According to R. J. Rummel, professor of political science at the University of Hawaii,
The genocide and gendercidal atrocities were also perpetrated by lower-ranking officers and ordinary soldiers. These "willing executioners" were fueled by an abiding anti-Bengali racism, especially against the Hindu minority. "Bengalis were often compared with monkeys and chickens. Said General Niazi, 'It was a low lying land of low lying people.' The Hindus among the Bengalis were as Jews to the Nazis: scum and vermin that [should] best be exterminated. As to the Moslem Bengalis, they were to live only on the sufferance of the soldiers: any infraction, any suspicion cast on them, any need for reprisal, could mean their death. And the soldiers were free to kill at will. The journalist Dan Coggin quoted one Pakistani captain as telling him, "We can kill anyone for anything. We are accountable to no one." This is the arrogance of Power.
Target killing of Intellectuals:
Along with the Mass killing, a notable pattern was Target killing of Intellectuals and professionals which started with ‘Operation search light’ at 25th March night. That dark night Pakistan army killed A number of professors from Dhaka University. However, the most extreme cases of targeted killing of intellectuals took place during the last few days of the war. Professors, journalists, doctors, artists, engineers and writers were rounded up by the Pakistani Army and the Razakar militia in Dhaka, blindfolded, taken to torture cells in Mirpur, Mohammadpur, Nakhalpara, Rajarbagh and other locations in different sections of the city to be executed en masse, most notably at Rayerbazar and Mirpur.
During the nine-month duration of the war, the Pakistani Army, with the assistance of local collaborators systematically executed
an estimated 991 teachers, 13 journalists, 49 physicians, 42 lawyers, and 16 writers, artists and engineers.
Even after the official ending of the war on 16 December there were reports of killings being committed by either the armed Pakistani soldiers or by their collaborators. In one such incident, notable filmmaker Jahir Raihan was killed on 30 January 1972 in Mirpur allegedly by the armed Biharis.
This was strategic killing to destroy the Bengali nation, intellectually and ideologically
Violence against Women/ Genocidal Rape :
Pakistani Major General Khadim Hussain Raja wrote in his book that Pakistani Commander-in-Chief General Niazi, in presence of Bengali officers would say ‘Main issharamzadiqomki nasal badaldoonga (I will change the race of the Bengalis)’. 
A witness statement to the ‘Hamdoor Rahman commission’ read "The troops used to say that when the Commander (Lt Gen Niazi) was himself a raper (sic), how could they be stopped?" 
The generally accepted figure for the mass rapes during the nine-month long conflict is between 200,000 and 400,000 Susan Brownmiller refers to an estimated number of over 400,000 
Pakistani sources claim the number is much lower, though havingnot completely denied rape incidents. 
Again, whatever the numbers- The Rape committed by Pakistan army was not individuals sexually driven act, but it was preplanned and part of Strategy to destroy the National Identity of Bengali’s .
It was Genocidal Rape, Part of Total Genocide.
a fatwa in Pakistan declared that the Bengali 'freedom fighters' were Hindus and that their women could be taken as the 'booty of war' They had a religious belief that ‘Pure’ Muslim will never stand against their Father, So they would rape Bengali Hindus & ‘Impure’ Muslim to produce a new ‘obedient’ generation.
There are eyewitness reports of the "rape camps" established by the Pakistani Army.
The US based Women Under Siege Project of the Women’s Media Center have reported the girls as young as 8 and women as old as 75 were detained in Pakistan military barracks, and where they were victims of mass rape which sometimes culminated in mass murder. The report was based on interview with survivors.
Australian Doctor Geoffrey Davis was brought to Bangladesh by the United Nation and International Planned Parenthood Federation to carry out late term abortions on rape victims. He was of the opinion that the 200,000 to 400,000 rape victims were an underestimation. On the actions of Pakistan army he said "They’d keep the infantry back and put artillery ahead and they would shell the hospitals and schools. And that caused absolute chaos in the town. And then the infantry would go in and begin to segregate the women. Apart from little children, all those were sexually matured would be segregated..And then the women would be put in the compound under guard and made available to the troops…Some of the stories they told were appalling. Being raped again and again and again. A lot of them died in those [rape] camps. There was an air of disbelief about the whole thing. Nobody could credit that it really happened!"
It was to escape this terrible slaughter that the refugees fled in millions to the safety of the neighbor Indian border. It is estimated that the population of Dhaka, a city of well over a million inhabitants, was reduced by some 25%. Jessore, formerly a town of over 100,000 was reduced to about 10,000 by the time of the liberation. A similar exodus occurred from other towns. The population of thousands of destroyed villages fled in their entirely. 
Indian government reports that around 8-9 million migrants took shelter in 829 refugee camps. According to National Geographic (Sept. 1972), the estimated number of Bangladeshi refugees was 10.0 million. Also, a large number of people were displaced within the country, estimated number was around 20 million (The UN in Bangladesh).
Again- Unlimited number were killed, looted and raped by Pakistan Army and their collaborators during escape. The story of the refugees did not end here. The refugees in India suffered from malnutrition and cholera. The refugees, submerged by fear and despair, faced a new color of death in the refugee camps in India. Despite the utmost effort of Indian Government to feed and keep them alive, refugees died of cholera and malnutrition. 
All these atrocities committed by Pakistan army was a clear Genocide.
We can summarize with a comment of R.J. Rummel "In 1971, the self-appointed president of Pakistan and commander-in-chief of the army General Agha Mohammed Yahya Khan and his top generals prepared a careful and systematic military, economic, and political operation against East Pakistan (now Bangladesh). They planned to murder that country's Bengali intellectual, cultural, and political elite. They planned to indiscriminately murder hundreds of thousands of its Hindus and drive the rest into India. And they planned to destroy its economic base to insure that it would be subordinate to West Pakistan for at least a generation to come. This despicable and cutthroat plan was outright genocide." 
References:1. Rummel, Rudolph. "Chapter 8: Statistics of Pakistan's Democide Estimates, Calculations, And Sources". Statistics of Democide: Genocide and Mass Murder since 1900. p. 544. ISBN 978-3-8258-4010-5 2. Debasish Roy Chowdhury (23 June 2005). "Indians are bastards anyway". Asia Times Online 3. "The events in East Pakistan, 1971: a legal study". ICJ.org , p 37 4. "World: Pakistan: The Ravaging of Golden Bengal". Time. 1971-08-02. ISSN 0040-781X. Retrieved 2016-03-31 5. U.S. Consulate (Dacca) Cable, Sitrep: Army Terror Campaign Continues in Dacca; Evidence Military Faces Some Difficulties Elsewhere, 31 March 1971, Confidential, 3 pp 6. DEATH BY GOVERNMENT, by R.J. Rummel New Brunswick, N.J.: Transaction Publishers, 1994 7. Khan, Muazzam Hussain (2012). "Killing of Intellectuals". In Islam, Sirajul; Jamal, Ahmed A. Banglapedia: National Encyclopedia of Bangladesh (Second ed.). Asiatic Society of Bangladesh 8. A Stranger in My Own Country: East Pakistan, 1969-71 (Oxford University Press, 2012) 9. Hamoodur Rahman Commission, Chapter 2, Paragraphs 32,34 10. Brownmiller, Susan, "Against Our Will: Men, Women, and Rape" ISBN 0-449-90820-8, page 81 11. Hamoodur Rahman Commission, Chapter 2, Paragraphs 32,34 12. Herbert L. Bodman, NayerehEsfahlaniTohidi 1998, p. 208 13. Hensher, Philip (19 February 2013). "The war Bangladesh can never forget". The Independent. London 14. "Why is the mass sexualized violence of Bangladesh's Liberation War being ignored?". Women in the World in Association with The New York Times 15. "1971 Rapes: Bangladesh Cannot Hide History". Forbes 16. "The events in East Pakistan, 1971: a legal study". ICJ.org 17. http://midnightowlblog.blogspot.com/2013/06/tears-of-bangladesh-1971-refugees.html 18. Mansur, Salim. "Genocide and Justice in Bangladesh". Gatestone Institute