The toddler siblings who died hours after being put to bed in their Bronx home Sunday night appear to have been beaten to death, the New York City medical examiner says. 

Olivia Gee, 2, and her 3-year-old brother Micha Gee, both died of blunt impact injuries to the torso, the medical examiner's office said Tuesday. 

Both children had histories of asthma and 911 was called after they allegedly had trouble breathing, but that condition apparently did not cause their deaths, the medical examiner's report indicates. Both deaths were ruled homicides.

No arrests have been made, though police earlier described an active investigation into the toddlers' deaths. 

Authorities have said the siblings' 31-year-old mother and her boyfriend had put the two to bed in the same room of their Van Cortlandt Park South home around 8:30 p.m. Sunday. The boyfriend woke up around 1 a.m. Monday and went to check on the kids, noticed they had breathing difficulty and called 911, according to the initial police report. 

Both kids were unresponsive when officers arrived; they were pronounced dead at a hospital. 

Olivia and her brother Micha had histories of asthma, and police said Monday it wasn't clear if they were looking at that as a possible factor in their deaths, though that was before the autopsy was completed. 

The boyfriend was interviewed by police and released, according to a law enforcement source. He has asked for a lawyer. 

Detectives hadn't been able to talk to the kids' mother, though, who was so distraught she had to be hospitalized, the source said. 

The siblings lived in an apartment at Amalgamated Houses, a tight-knit co-op community, according to people who live there. The children's grandmother works as director of education for the co-op and has lived there 25 years, building manager Charles Zsebedics told NBC 4 New York. He said Monday the children were "angelic and happy," and that "anyone that sees them knows they are well taken care of." 

Learning on Tuesday the children had been killed, he said, "We're as shocked now as we were yesterday, this is the unthinkable. Our worst fears were realized, we couldn't imagine this is something that could actually happen. We are very, very sorry for the entire family."