About a week before free agency started the San Diego Chargers released DE Luis Castillo, who had been with the team ever since they made him a first round pick in the 2005 NFL draft. Shortly after that, news came out that the Kansas City Chiefs had him in for a visit. There were also rumors that the Dallas Cowboys would be interested, though it's not clear if a visit ever took place.
This shouldn't be a huge surprise because the Chiefs and Pats are often interested in the same players. The Pats inked DT Jonathan Fanene to a multi-year contract in free agency so he's their "splash" in free agency this year, outside of the recent deal Brandon Lloyd received.
If the Chiefs still have interest in Castillo even after his visit, I'd bet they're waiting for the market to settle down to see what his real value is, and which other teams have interest. Rapoport reports there's another team that has interest but doesn't name them. The infamous "mystery team" strikes again.