He was even more surprised when he learned that Warf's ex-husband, Aaron Desjardins, was charged in her murder.
Coughlin, a Portsmouth lawyer, was representing Desjardins while he and Warf ironed out the details of a parenting plan for their 11-month-old son, William, in the Brentwood Family Court.
Coughlin was hired just after their divorce was final in February 2012 and says he never saw any serious problems between the two.
They may have disagreed at times like many divorced couples, but Coughlin said it was nothing unusual.
"I hear about these things happening, and sometimes when I'm involved in a particular case I wonder if something bad might happen because of the nature of my client or the nature of the opposing party," he said. "This case didn't have that. It's surprising that he might somehow be involved."
The last time Coughlin spoke with Desjardins was a few weeks before prosecutors say he killed Warf by slitting her throat.
The body of the 36-year-old mother who worked at Exeter Hospital was discovered on the second floor of the abandoned City Concrete factory on Hampton Road in Exeter on March 7. Firefighters found her body while responding to a fire that prosecutors say was intentionally set, though Desjardins hasn't been charged with arson.
Just a few days after telling reporters he had nothing to do with her murder and that someone else had done it, Desjardins, 36, was arrested at gunpoint near his Epping home Tuesday and charged with first-degree murder.
Coughlin said he believes Warf and Desjardins were still seeing a co-parent counselor at the time of the killing and had a hearing scheduled in May.
"They were working on the minutia, the logistics of the parenting time that they would spend with William, but they had pretty much equally divided it, and they were trying to figure out when transfers would occur and things like that," Coughlin said.
Before his arrest, Desjardins told the New Hampshire Union Leader that he and Warf had "come to full agreement" on custody of their son.
"We were just going to put the ink on the paper," he said at the time, suggesting that all was well between him and Warf.
Unlike some couples, Warf and Desjardins didn't seem to have a problem getting together to work out their issues.
"They could meet in the same room. There were no domestic violence aspects of the case. No restraining orders," Coughlin said. "If it turns out that he was aggressive toward her during this event I certainly never saw evidence of that when I observed them dealing with each other."
At times, even Desjardins' new wife, Sarah, would attend meetings with Coughlin when Warf was also present. Court documents hinted at some tension between the two women in the past, but Coughlin said Sarah was "very helpful with him in parenting William."
According to Senior Assistant Attorney General Susan Morrell, William is now being cared for by other family members while Desjardins remains held without bail at the Rockingham County jail. He is due back in court for a probable cause hearing on March 22 at the 10th Circuit Court in Brentwood.