The trade announced Monday brings Najera back to Dallas, where he was a fan favorite in his first four NBA seasons. He played in 39 postseason games with the Mavericks, including 19 in 2003 when Dallas lost to San Antonio in the Western Conference finals.
"We obviously think he can help our team," Mavericks coach Rick Carlisle said Monday. "He's had some injury things go on this year, but my understanding is that he's been doing better, so we'll see. He's going to be who he is. I've never coached him, but my perception is he plays one way, and that's full-speed ahead. Guys like that, you always want to have as many as you can on your team."
The native of Mexico was traded to Golden State in the Erick Dampier deal in 2004 and was later sent to Denver. He averaged 3.8 points in 13 games in his second season with the Nets.
NBA front-office sources told ESPN.com on Friday night that the Nets agreed to use a trade exception to absorb the $2.4 million expiring contract of Williams, which clinched the deal. Dallas sent Williams away from the team last season over concerns about his professionalism and did not let him return this season.
The Nets made room for the trade by waiving former first-round pick Sean Williams. Sources said the Nets would also waive Shawne Williams as soon as they obtain him.
Humphries averaged 5.2 points in 25 games for the Mavericks. Williams hasn't played for Dallas since last January.
The teams had been discussing the deal for several days but talks appeared to break down when the Nets shifted their focus earlier in the week to the buyout of veteran guard Rafer Alston and the acquisition of reserve guard Chris Quinn from Miami.
Although Najera remains popular locally after a successful four-season stint as an energy guy to start his career, Dallas' motivations for making this deal were largely financial.
The Mavericks have been trying to move Shawne Williams for months and shedding his contract along with Humphries' deal will save Dallas nearly $2.5 million in 2009-10 salary, which computes to an overall savings of nearly $5 million when adding in the Mavericks' luxury-tax obligations.
The Nets, by contrast, were willing to take on Humphries -- and the extra $700,000 he's guaranteed next season compared to Najera -- because they're looking for younger players who can supply more hustle and effort to help the team survive the second half of what is threatening to be a historically dismal season.
At 3-32, New Jersey is on a pace for only seven victories, which would make them the worst team in NBA history, replacing the Philadelphia 76ers who posted a 9-73 record in 1972-73.
ESPN.com senior NBA writer Marc Stein, ESPNDallas.com's Jeff Caplan and The Associated Press contributed to this report.