Halman, 24, was found stabbed to death at a house in Rotterdam, Netherlands, on Monday. Reports indicate that his 22-year-old brother was arrested as a suspect.
The Haarlem, Netherlands, native was coming off his rookie season in the Majors after splitting time between Triple-A Tacoma and Seattle, appearing in 75 games overall.
Police were called to the house Monday morning and found Halman bleeding from a stab wound, according to Rotterdam police spokeswoman Patricia Wessels. Paramedics were unable to revive him.
"He is under arrest and right now he is being questioned," Wessels told the Associated Press of Halman's brother, whose name was not disclosed. No charges have been filed in the case. "It will take some time to figure out what exactly happened."
Major League Baseball Commissioner Bud Selig released a statement Monday afternoon regarding the news.
"Today Major League Baseball mourns the passing of Greg Halman, a member of the Seattle Mariners organization since 2004," Selig said. "The loss of a talented 24-year-old young man like Greg, amid such tragic circumstances, is painful for all of us throughout the game.
On behalf of Major League Baseball, I send my deepest condolences to the entire Mariners organization and to all those whose lives were touched by Greg."
"We are shocked and incredibly saddened by the news this morning," Halman's agent, Greg Nicotera, told MLB.com. "Hopefully in time we will all be able to come to terms with the tragic loss of such a passionate, good-hearted, generous and faithful young man. Our thoughts and prayers are with Greg's family, friends and loved ones. This hurts."
"The Mariners family is deeply saddened by the tragic death of Greg Halman," the Mariners said in a statement. "Greg was a part of our organization since he was 16, and we saw him grow into a passionate young man and talented baseball player. He had an infectious smile that would greet you in the clubhouse, and he was a tremendous teammate. Our thoughts and prayers go out to Greg's family."
Tacoma Rainiers Team President Aaron Artman released the following statement:
"Greg was a huge part of the Rainiers during his time here in Tacoma, and played a pivotal role -- on the field -- in our run to the 2010 Pacific Coast League Championship. ... He had a huge smile on his face, every day, and his enthusiasm was infectious. He just had a way about him that made our front office staff and fans see a guy who clearly loved what he was doing. ... We miss Greg already, and our prayers go out to his family, friends, teammates and the Mariners organization."
Halman, who played for the Netherlands in the 2009 World Baseball Classic, had returned home this offseason to prepare for the 2012 season. He participated in several baseball camps for children two weeks ago that were organized by Orioles pitcher Rick Van den Hurk, a fellow Netherlands native. The camps were part of the European Big League Tour.
The right-handed hitting center fielder batted .299 with three homers, 15 RBIs and 11 steals in 40 games for the Rainiers before seeing time in 35 Major League games as a rookie with Seattle, where he went 20-for-87 (.230) with six RBIs. He finished the season in the Minors, hitting .300 in August and .364 in September.
"The only thing I can say right now is we are deeply shocked," said Robert Eenhorn, the technical director of the Dutch baseball association, to the AP. "All our thoughts are with his family and how they are going to have to deal with this tremendous loss."
Halman was a player of note in the Mariners' system, posting big power numbers the last few years at several levels. He hit 29 homers and 83 RBIs in 2008, finished with 25 homers in 2009 as a Southern League All-Star and hit a career-high 33 longballs in 2010 at Tacoma.
Perhaps his best season was '08, when he hit .272 with a career-high 31 steals to match his career-best 83 RBIs at Class A Advanced High Desert and Double-A West Tenn before going on to earn Rising Star status in the Arizona Fall League.
Halman enjoyed his best day in the Minors on June 1, 2010, when he homered twice and knocked home a career-high seven runs against Sacramento. He had another two-homer effort two days later and added a two-homer, five-RBI night on July 18.
The outfielder signed with Seattle as an international free agent in June 2004 and made his professional debut a year later on June 23, 2005, with the Rookie-level Arizona League Mariners. He had 118 homers in 572 career Minor League games and made his Major League debut Sept. 23, 2010, with Seattle. His first big league hit came Sept. 27 against Texas and his last on July 19, 2011, against Toronto.