A lioness killed a forest guard while a lion escaped from its enclosure in the Sanjay Gandhi National Park on Tuesday evening, officials said.
The attack took place due to the alleged negligence of the forest guard as he left the door of the enclosure open during the evening feeding time of the lions, an official said.

According to an official, Harichand Gangwan, the forest guard, had gone to feed the five lions and lionesses in the enclosure at around 6 p.m. but he apparently forgot to shut the trap door separating the wild animals and the feeding area.

Seizing the opportunity, one of the two lionesses rushed in and pounced on Gangwan, even as a couple of other forest guards watched in horror.

Regaining their composure, one of the guards tried to shut the trap door to prevent the other three lions from escaping. But one of them proved too fast and bolted out.

Additional armed forest guards were summoned from the national park headquarters located around two kilometres away and they tried to chase the 'killer' lioness away and collect Gangwan's body.

But the lioness, growling ferociously, refused to let go of the body for nearly an hour. The forest guards later shot a tranquilizer and immobilised her.
However, till late Tuesday they could not retrieve Gangwan's body since one lion was still at large in the national park, the official said.

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Source : freepressjournal

Please explain to me the emboldened parts.

Though I know "bolt out" means "east fast" and I'm not sure here "them" refers to whom "one of the guards or one of the lions".

one of them refers to the lions

bolt out = to run away quickly (from the enclosure; hence the out in bolt out)
I think it's exactly this.

A crossbow fires a bolt, to "bolt out" is the adj to describe something as fast as a bolt.