I never went to East Pakistan when it was part of Pakistan. In fact, there was some talk of sending me to Chittagong a month before the massacres of Memons and other West Pakistanis began (yes, it was the Bangladeshis who started it). Fortunately my bosses decided I was needed in Karachi. In the month that the rebels had held Chittagong, almost all the Memons (including a distant relative) were slaughtered. Some managed to escape to West Pakistan and it was from them that we learned that the situation was really very bad (contrary to what the Establishment was telling us at the time). When I went there twenty four years back, I met a few who were staunchly pro-Pakistan but most hated it. This was because they'd grown up believing that millions of their countrymen had been killed deliberately by Pakistanis in the civil war that preceded the break-up of the country.
I met a former civil servant who had served in Islamabad before the break-up. He was now based in Canada, and asked me why Pakistani leaders were not apologizing for the so-called genocide of Bengalis. I asked him what proof there was that there had been a genocide.
I met another Bangladeshi who quoted a discredited Pakistani journalist (Tony Mascarenhas) who had claimed that millions of Bengalis had been killed. I met a waiter in Dhaka Club whose father had been shot by a soldier.
Perhaps a few thousand may have been killed, but then there were an equal number from our side who had also been slaughtered by them. I remember two Memon girls (both students in a medical college) who were taken away by the rebels and were never seen again (their mother went mad).
So, in my opinion, as atrocities were committed by both sides, the question of apologizing does not arise.
