It is preferred to attempt alternative options to lethal force where practical, but it should be weighed against the need to immediately stop/arrest the suspects, the severity of the crimes being pursued, and the need to protect yourself, another innocent, or the station at large.
You are still expected, to the best of your ability, to attempt to limit the amount of collateral damage and attempt to prevent the suspects from dying. If enough of the suspects were to abandon their attack on you after you deploy lethal force it may be appropriate to de-escalate to something less-lethal instead of further pursuing the suspects with lethal force after immediate danger has passed, however this is up to the totality of the circumstances.
This answer is not intended to limit the ability of security to use lethal force when they otherwise would be able to.
This clarification is based on the previously approved answer