(CNN) -

He was a basketball-loving kid from the Midwest who turned into a jihadi fighting terrorists in Syria -- and dying there.

Exactly what spurred Douglas McAuthur McCain's metamorphosis remains murky. But while his radicalization and death have stunned loved ones back home, his actions abroad have raised fears that other Americans may follow suit.

Here's what we know about the 33-year-old man who died while fighting for ISIS, the radical militant group that has captured swaths of Iraq and Syria and spawned major concerns in the United States:

He grew up in Minnesota

McCain grew up in the Minneapolis suburb of New Hope, his friend Isaac Chase said.

The two lived in the same New Hope apartment building and became fast friends.

"When I first moved here, I didn't know anyone, so I went to the park and I would see him and his brother and a bunch of other people playing basketball, and he asked me if I wanted to play," Chase said.

"We just hung out pretty much from 10 o'clock in the morning all the way until nighttime. We'd just play basketball and talk. ... He was an older guy that I looked up to. He was actually a good dude."

Chase remembers McCain as a nice, quiet young man, but one who was looking for purpose in life.

When Chase joined the Air Force in 2007 and served in Iraq, McCain was impressed that his friend was making something of his life and wanted to do the same, Chase said.

But after learning that McCain died while fighting for ISIS, which is trying to establish an Islamic state across Iraq and Syria, his friend was bewildered.

"It just hurts a little bit knowing that if he was over there and I was over there at the same time, we would've been going against each other," Chase said. "That's what hurts the most because he was a good person, and I just don't understand why anyone would do anything to the U.S."

His family is stunned

And he was raised by good parents, Chase added. He said McCain's mother attended church regularly, while the father is deceased.

Ken McCain described the nephew he knew as "a good person, loved his family, loved his mother, loved his faith" -- the latter being a reference to Christianity he practiced before his conversion to Islam several years ago.

The family wasn't alarmed by his conversion. But McCain's Facebook posts sympathetic to ISIS got relatives' attention, the uncle said.

"We are devastated, and we are just as surprised as the country is," Ken McCain said of the news his nephew had become a jihadi in Syria.

But not every family member believes Douglas McCain joined ISIS, a group with tactics so brutal even al Qaeda has disowned it.

"We're from Chicago. We grew up in Minnesota," his cousin Kenyata McCain told CNN affiliate KARE. "He's not a terrorist. That's crazy."

"His religion was very important to him, but those people -- the ISIS people -- they don't represent what my cousin's beliefs are or were at all."

Kenyata McCain -- who said Douglas commented about her sons growing up on a Facebook photo a few days before his death -- wondered if her cousin may have gotten caught up in the wrong crowd.

"Why was he in Syria? ... What kind of people was he hanging around? I feel like maybe it was the people he was hanging out with because that's not who he is. He's not ISIS," she said.

Spent time in California, Sweden, Turkey

Douglas McCain didn't take a straight path from Minnesota to Syria, from Christianity to an extreme brand of Islam, from "good person" to accused terrorist.

Physically, he moved around some as well.

That includes time in Southern California, where he attended San Diego City College, according to spokesman Jack Beresford.

At the beginning of this decade, McCain also spent time in Sweden.

An acquaintance of his in that Scandinavian nation, Kevin Tornstrom Kohlin, remembers him as "a really good basketball player" and a "fun guy who spread a lot of good energy."

"I never noticed him giving any bad energy, at all, to anybody," Kohlin said from Vasteras, Sweden. "Everybody who met him, of those I know, remember him the same way."

McCain appeared to have no problem with anyone's religion -- including that of Kohlin, who is Christian.

While all his stops aren't publicly known, uncle Ken McCain did say that his nephew was in Turkey when he last touched base with him a few months ago.

Not coincidentally, Turkey borders Syria.

U.S. government had been monitoring him

McCain had several run-ins with local law enforcement in Minnesota since 2000, according to the Hennepin County Sheriff's Office.

These include arrests for disorderly conduct, speeding, driving after revocation, theft by swindle and giving an officer false information. And in 2003, he paid a $250 fine after pleading guilty to having marijuana in a motor vehicle, according to court records.

Still, these were minor issues, certainly not matters of national security.

In the early 2000s, though, Douglas McCain did come to the federal government's attention, according to a U.S. official.

He was associated over the years with numerous people who authorities were watching -- including one from Minnesota who ended up dying in Somalia while fighting as a jihadi -- the official said.

But there was no indication that McCain was involved in anything nefarious during his time in the Midwest.

Things changed, though, as the years went by.