Const. David Hsu was called in to look for witnesses after the baby was found abandoned in the Calgary trash bin in October 2010.
He testified Tuesday that he thought Meredith Borowiec was just an "onlooker" when he saw her sitting, barefoot, wearing pyjama bottoms and with a blanket wrapped around her waist.
Hsu said Borowiec told him she was at home ill that day but had been told by her boyfriend that a baby had been found in the Dumpster.
When he saw blood on the blanket by the woman's leg and on her coat sleeve, Hsu became suspicious that she was the child's mother.
"I thought she was a suspect," said Hsu. "The fact she had blood on her leg and her sleeve was suspicious."
Borowiec, 31, is charged with two counts of second-degree murder in the deaths of two of her newborn children in 2008 and 2009 and before the infant was rescued from the garbage in 2010.
The Crown wants the baby found in the trash ruled as similar-fact evidence so it can be used in the murder trial, which is being heard by a judge without a jury.
A separate attempted-murder trial is scheduled for this fall dealing with the child in the garbage.
Hsu said Borowiec told him she was having a heavy period and had been having them since she had a miscarriage in July 2009, which is the same time the Crown alleges she killed one of her newborns.
Hsu called for paramedics to examine Borowiec and accompanied her in the ambulance on the way to hospital. Paramedics were concerned that she had lost a significant amount of blood and noticed stretch marks on her abdomen.
Hsu said he received a call from his superior while on the way to hospital and was ordered to read Borowiec her rights on a charge of child abandonment.
"She said, 'I don't really have anything to say. What's going to happen to me?'" he said.
She then started crying.
"EMS asked, 'When did you deliver?'" Hsu recalled.
"The female said, 'About noon. I'm sorry.'"
Emergency medical technician Heather Karst said Borowiec was calm until she was read her rights.
"She started crying. She mostly seemed scared," said Karst.
Hsu told the judge that he waited at the hospital and gathered Borowiec's bloody clothes and blanket as evidence.
The defence suggested Hsu wasn't concerned about the woman's welfare but only accompanied her to hospital so he could "overhear her" in the ambulance.
"That wasn't my intent," said Hsu.
The trial is scheduled for six weeks.
The child has recovered and is healthy.
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