The NYPD has revealed that one of the officers slain in Brooklyn this past weekend was filling in for a co-worker who was late that day. Officer Wenjian Liu was killed along with Rafael Ramos by Ismaayil Brinsley as they sat in their police car. 

The New York Daily News reports that Liu, 32, volunteered to fill in for the 40-year-old Ramos' usual partner, who had phoned a desk sergeant at the 84th Precinct to say that he was running late: 

Liu’s selfless act meant that he died alongside Officer Rafael Ramos when a crazed gunman opened fire on their patrol car in Bedford-Stuyvesant on Saturday, executing the pair simply because they were cops.

This is a difficult time for both of our families, Liu’s devastated widow, Pei Xia Chen, told reporters in brief remarks Monday during which she expressed her condolences to Ramos’ widow and children. But we will stand together and get through this together.

A police source told the Daily News that Liu "[W]asn't supposed to be there." Another source said that Ramos' former partner is overcome with guilt.

"He’s beside himself," the source told the Daily News. "It’s very, very hard for him."

[via New York Daily News]