I've thought the same thing. That FBI and LE released them because they didn't have enough rock solid evidence yet (waiting for DNA reports and Land Rover results).
And, I think LE has been releasing a fair amount of information that could make the perps increasing frightened, and LE and FBI would love for them to get really nervous and make a mistake.
And, I also think that they were waiting for DNA to come back from the property, the gloves and possibly something in the Land Rover. LE and FBI want very solid evidence to link them directly to the crime in order to get a conviction.
But that Friday night SWAT raid was serious. Enormous amount of vehicles and LE/FBI presence. In order to get a federal warrant, FBI have to present a lot of compelling evidence. Federal warrants are a big deal and there was a great deal of information in the warrant that led to the judge issuing the warrant. Don't think it was a mistake that they zeroed in on that man.
JMO