The NYPD tell the New York Daily News that officer Wenjian Liu had volunteered to fill in for the man normally partnered with officer Rafael Ramos the day he was shot and killed by Ismaaiyl Brinsley in Brooklyn's Bedford-Stuyvesant neighborhood. Ramos' usual partner was running late that day.

Ramos' partner, the Daily News reports, called into the NYPD's 84th Precinct last Saturday to say he was going to be late; brass put out a call for someone to cover him, and Liu apparently volunteered. "He wasn't supposed to be there," a police source told the tabloid.

The officer whom Liu filled in for has not been identified, but the Daily News' sources tell the paper, "The kid is very, very distraught. He's beside himself. It's very, very hard for him."

In a statement released yesterday, Liu's family said this week (on Christmas Eve) would have been the 20 year anniversary of his immigration to the United States from Guangzhou, China.

"This is a difficult time for both of our families," Liu's widow, Pei Xia Chen, told reporters at press conference Monday, fighting back tears. "But we will stand together and get through this together." Liu and Chen had just married in September.

[Image via NYPD]