Any long range mission into deep space requires careful psychological testing of all crew, the pressures of enforced isolation and constant proximity can drive people to terrible acts of violence.
Not all testing is perfect.
From Pinbacker in Sunshine to Weir in Event Horizon, anyone would think deep space missions were intentionally looking for command crew with psychological problems. Although the rescue crew are keeping it together at this point
the same could not be said for the Omega's original captain.
The first Challenge Deck expansion for SSO, First Captain, tells the story of the Omega's original captain trying to wipe out your rescue team. He does this by a cat
and mouse assault on the crew's morale along with a more direct assault on the bodies of anyone who spends too long alone in the ship, picking off lone crew members.
Crew can buddy up to cover each other's backs and lessen the effects of Morale loss while trying to recover their nerve, but in the end desperate times call for desperate measures and a homicidal maniac on the loose certainly qualifies.
If the captain can't be tracked it means he's not wearing his suit. No suit means no personal oxygen supply. Dump the air, open the air locks and flush the mad man into space. Its high risk, every miscalculated breath will mean a crew member's death.
Either way, with a dead rescue crew or the ship's atmosphere dumped into space, the result will be the same.