The man they were referring to is Warren Weinstein, who was reportedly been held since August.
al-Zawahiri has a list of demands that would ensure Weinstein's release, although these demands seem to be too hard to give considering the threat it poses to the US and the world at large.
In a video released on jihadist internet forums, al-Qaeda leader Ayman al-Zawahiri claimed that the organization had kidnapped American aid worker Warren Weinstein, who was taken by armed men from his home in Lahore in August.
"I tell the captive soldiers of al-Qaeda and the Taliban and our female prisoners held in the prisons of the crusaders and their collaborators, we have not forgotten you and in order to free you we have taken hostage the Jewish American Warren Weinstein," Zawahiri said. In exchange for Weinstein's release, Zawahiri demanded the lifting of the Israeli blockade of the Gaza strip, a halt to U.S. bombing of al-Qaeda and allied groups in Pakistan, Afghanistan, Somali, Yemen, and Gaza, the closure of the prison at Guantánamo Bay, and the release of al-Qaeda prisoners; he also confirmed the death of key al-Qaeda figure Atiyah Abd al-Rahman, who was reported killed in a U.S. drone strike in August.
Everyone knows by now that the terrorist organization relies on the tactics of fear and intimidation, so naturally, when they want something, they will go to any length to get what they want, including hostage of a helpless civilian, and killing of innocent lives.
It should go without saying that if you want some of your men released from captivity, the worst possible thing to do is capture someone from another country. The Taliban nor the al-Qaeda is not interested in diplomacy. It is more interested in using the age old "primitive" tactics of fear and intimidation to get what they want. Unfortunately, it's unlikely to happen.
It is more likely President Barack Obama won't even give a second glance to al-Zawahiri's demands. They are, according to a commentary, of a ridiculous nature. The tactic of saying that Mr. Weinstein's life is in Obama's hands is just another Al Qaeda tactic of trying to force a hand that somebody isn't going to play. The United States does not have a history of negotiating with terrorists. It is highly unlikely that will happen now. Given the list of demands, it is even more ridiculous. They are asking for the exchange of hundreds of suspected terrorists for one businessman who was trying to merely help businesses in Pakistan.
al-Zawahiri was a physician before he became an Islamic theologian, surely, under the oath of a physician, he would have to consider Weinstein's health, as that oath was sworn to save someone's life, most especially of the sick. But it appears he had thrown away the noble part of him in exchange for a theology (while not literally speaking of general Islam) that's bent to harm others around him.