Of course they did. Egypt definitely does not want any reports of what crooked shenanigans their government is and was involved in getting out to the outside world and that is exactly what al-Jazeera was doing, airing Egypt's dirty laundry for all the world to see and know about firsthand.
The Egyptian government most likely targeted the former Al Jazeera employees sentenced to death. Egypt has cracked down on opposition; including rights like freedom of speech and freedom of the press. The government may be making an example by sentencing the former Al Jazeera employees to death; kind of a way of telling others to be careful what they say in the media.
Al Jazeera is known to expose intimate details about how governments are run around the middle eastern region. Egypt has been known to suppress journalists that are vocal against their government policies. Serious penalties have included torture and even death. Because of who they worked for and their occupation, the journalists were sentenced to death for no other than who they worked for and what their job entails.
Egypt recently sentenced a number of former Al Jazeera employees to death. These individuals had an association with a news organization that Egypt has sought to silence. It is for that reason those former employees were specifically targeted. Just another unfortunate example of the severe lengths that governments will go to in order to censor the news.