WINNIPEG -- Immediately after a letter bomb exploded inside the small family-law firm where Maria Mitousis worked, she slumped in her doorway, covered in blood and begged a colleague not to leave her side.

"I heard a large bang and (there was) a scream, followed with a second scream," Connie Petersen, managing partner at the Petersen King law firm in Winnipeg told a courtroom Wednesday.

"Maria was walking out of her office ... she slid down the side of her door frame."

Two co-workers called 911 and were told to evacuate the office, Petersen added.

"Maria said, 'Don't leave me. Please comfort me.' There was a lot of blood going down from her throat."

Mitousis would undergo surgery in the hours that followed the July 3, 2015, explosion. She lost her right hand in the blast and suffered severe injuries to her face, torso and legs.

Police later charged Guido Amsel, the former husband of one of Mitousis's clients in a divorce case. He is also on trial for sending other letter bombs that July to the workplace of his ex-wife, Iris, and to another law firm that had represented Amsel. Neither of those bombs detonated before police found them.

Amsel, 51, is also accused in a 2013 explosion outside the home of his ex-wife that did not cause any injuries. In all, he faces five counts of attempted murder and several explosives-related charges. He has pleaded not guilty and is being tried by a judge alone.

The trial has already heard from police officers who say the package that exploded in Mitousis's office contained a voice recorder with an explosive compound designed to detonate when the play button was pressed. There was also a note instructing her to press play, they testified.

The trial also heard Wednesday from Karlee Kaplan, a legal assistant who worked on the law firm's reception desk. She said a package had come in the mail for Mitousis the day before the explosion while she was out of the office, so Kaplan placed it on the lawyer's desk.

Kaplan said Mitousis returned the next day, went into her office and a few minutes later there was a loud noise. Kaplan ran to the office and saw Mitousis on her hands and knees.

"Her face was covered in blood. Her clothes were covered in blood," she testified.

Amsel's lawyer, Saheel Zaman, has questioned how police officers handled evidence collected and whether they properly secured the scene to avoid it being contaminated by others.

At one point Wednesday, he asked Petersen whether, as managing partner, she had even been told by Mitousis of any animosity or problems stemming from the Amsel divorce.

"You'd agree with me that (Mitousis) didn't bring up the Iris Amsel file as problematic?" Zaman asked.

"No. Not that I can recall," Petersen replied.