FOXBORO — The new hire was three years out of college when he first stepped behind the curtain at Gillette Stadium. A 25-year-old personnel assistant, the Patriots gave him plenty of grunt work in his first NFL job in 2001.

It didn’t take long for the rumors start.

Did he leave the office last night? Was he working out in the gym at 3:30 in the morning?

Yes, Nick Caserio was.

The kid from Lyndhurst, Ohio, was all in from the moment he started working for the Patriots. Caserio routinely put in 22-hour workdays when he arrived. For those around him, it was obvious that big things were in store. Just ask Tampa Bay Buccaneers general manager Jason Licht, who worked with Caserio in 2001.

“When he starts something he’s going to finish it,” Licht said. “I remember the whispers started going around the office in a few weeks that Nick was in there until 3 a.m. or Nick was getting in his workout in at 3:30 a.m. so he could spend the rest of the day working on something. That was very early on in his career. After you saw the quality of the work he was doing, you knew that this kid was pretty special.”

Fast forward 16 seasons in Foxboro and Caserio has climbed through the ranks. He’s been an offensive assistant (2002), area scout (2003), director of pro personnel (2004-2006), wide receivers coach (2007) and the team’s director of player personnel since 2008.

It’s a rise that Licht saw firsthand. After leaving the Patriots in 2003, he returned in 2009 as the team’s director of pro personnel. That hardworking kid he first saw in 2001 became his boss.

“I felt like when I went back, I wanted to take more advantage of the situation to work for a guy like Bill [Belichick],” Licht said. “It can only help you. It was like going to grad school. Nick, he’s a professor now.”

Now 41, Caserio's fingerprints are all over a team that’s one win away from Super Bowl LI. Caserio’s meteoric rise under Belichick is not surprising to those who’ve worked with him.

Rapid rise

After graduating from John Carroll University outside of Cleveland, where as a quarterback he set 16 school records, it didn’t take Caserio long to get to the NFL.

He worked as a graduate assistant for Saginaw Valley State (1999-2000) and Central Michigan (2001). He was only at his second stop for a matter of months before he walked into coach Mike DeBord’s office to let him know that he was heading to Foxboro.

“I made a joke and said something like, ‘Is it the Saginaw Patriots?’ ” DeBord said. “It was amazing. [Former assistant and current Tennessee coach] Butch Jones said, ‘You watch. That guy is going to be a general manager in that league.’ Everybody saw what kind of guy he is. He’s very personable. He’s a hard worker and communicates very well.”

Randy Awrey gave Caserio his first football job out of college at Saginaw Valley.

Part of Caserio’s responsibilities was recruiting. Often, with younger coaches, Awrey found that they’d bring him players who were good on the field, but came with off-field baggage. That was never the case with Caserio. In two seasons, he showed he had a unique eye for recruiting and impressed with his maturity and knowledge of the game.

After going 4-6 that first season, Saginaw Valley went to the Division II playoffs in five of the next six seasons.

“He definitely was a part of doing that at that school,” Awrey said. “I knew he was going to be a fast riser on the field because when you take a smart, young, personable person and you put them in this game, they usually move up pretty quick.”

“A lot of people in life can work hard but you got to have that passion. You want to put the two together, now you’ve got what Nick Caserio is.”

Caserio wasn’t the first or last kid from a small school hired by Belichick. The Patriots value assistants from smaller colleges. They found that people at places like Saginaw Valley, for example, had fewer resources, which forced younger assistants to step up and take on more responsibility.

“Part of it was his background,” said former Patriots executive Scott Pioli, now assistant general manager for the Atlanta Falcons. “Even though that background at Saginaw Valley doesn’t sound very [appealing], it’s not LSU, but he learned a lot. He knew football.”

Quick study

Caserio stood out in his first season with the Patriots. He did so well that his job responsibilities were expanded to include film breakdown and scouting-report preparation for the offensive coaches.

Pioli, the Patriots former director of player personnel, worked with Caserio for eight seasons before becoming the Kansas City Chiefs GM. His protege excelled not only in the personnel department, but also as a scout and on the coaching staff. In 2007, Caserio was in charge of a receivers group headlined by Randy Moss.

“Nick is one of the hardest workers. He’s as hardworking as anybody I’ve been around in the game,” Pioli said. “He’s genuinely passionate about the game of football. He’s very smart. He’s not afraid to say, ‘I don’t know or I don’t have an answer’ and then he immediately goes to work to find the answer.”

As Caserio worked his way up, he left an impression on his peers with his integrity and brutal honesty. There are no surprises when it comes to working with Caserio. He’s not in it for personal glory. And if you’re going to work for Belichick, that’s how it has to be.

In the Patriots organization, even in the front office, “do your job” is heard repeatedly. Caserio took it to heart.

“Another thing I respect about Nick is part of his intelligence has come by virtue of hard work,” said Pioli. “Sometimes people think those things need to be mutually exclusive. You’re either intelligent or hardworking, he’s intelligent and he’s hardworking which makes him even smarter. The things that he doesn’t know, he immerses himself into to learn.”

It’s also sink or swim when working under Belichick. It’s challenging, but in the personnel department, Caserio has autonomy and is expected to make decisions. Belichick fosters an environment where he wants differing opinions and healthy arguments.

“Nick is definitely not someone who is just going to agree with his boss, Bill in this case,” Licht said. “I think this is really why Bill has entrusted him to run the personnel department for him because he knows he’s getting original thoughts. He knows he’s getting a pure evolution and he’s not getting someone to tell him what they think he wants them to tell them. Nick is very cut and dry with his opinions.”

Multiple roles

What exactly does Caserio do for the Patriots? The answer isn’t simple. And the truth is, he does a little of everything.

When practice starts, it’s easy to spot him. Like an assistant coach, Caserio is in the middle of the chaos. He’s usually seen wearing white football gloves with a football in his hands. He soon starts throwing passes to the wide receivers as drills begin. He’ll pause for a moment as he releases the ball, showing off his throwing form.

When the games start, he’ll be in a box high above the field, wired into offensive coordinator Josh McDaniels’ headset for the duration of the game.

“He’s been in the press box I think every game I’ve ever called here,” said McDaniels, who played at John Carroll with Caserio and helped bring him to the Patriots. “He’s the one that usually talks to me about the hash and the down and distance. … Nick seems to have an endless list of those things and that’s because he does everything well. Nick deserves a lot of credit for a lot of things that he does. He helps me tremendously.

“He’s always helped me tremendously, whether it’s in preparation for the next opponent, next season, in-game. His talent is vast. His impression on each game or each week or in the offseason is significant.”

McDaniels’ sentiments are echoed by many who’ve worked with Caserio. It was similar with Houston Texans coach Bill O’Brien, a Patriots offensive assistant when Caserio was the receivers coach in 2007.

“I’ve learned a lot from Nick. I learned a lot about the NFL. I learned a lot about coaching and evaluations,” O’Brien said. “Nick does everything there. He’s a very loyal guy.”

When Licht rejoined the Patriots in 2009, one selling point was working with Caserio again.

“From the outside, it may look like it was a little unique situation where he was a scouting assistant when I was there before and then now, he’s my boss,” Licht said. “But I wouldn’t have accepted the opportunity if I didn’t think it was something I thought was going to be good. I actually learned a lot from Nick. … I really admire him and look up to him.”

Caserio’s reach with the Patriots extends far, but his impact as the team’s director of player personnel has been vital. Belichick signs off on all moves, but it’s Caserio and his team that identifies talent in each draft, free-agent period and looks for trade targets.

Around the NFL, Caserio is identified as a top GM candidates, but luring him away from the Patriots has so far been impossible. San Francisco tried this year and Miami before that.

“You brought up no one knows what he really does,” Licht said. “But he’s doing the same things I’m doing here [with Tampa Bay] as the general manager, which is overseeing the scouting department and picking the players. Some people get caught up in the power, wanting the GM so they can have the title and things like that. Nick is caught up into winning.”

It’d be hard to find a better fit for the Patriots.