There are many bands named Decomposed, most all of them death metal bands.
1) A death/doom metal band from UK formed in 1990 and released two demos, an EP in 1992, and an album 'Hope Finally Died...' on Candlelight records, 1993. Broken up. Three members went on to form a progressive metal band called Collapse which released one demo in 1995 and then broke up.
2) A currently active Swedish old school death metal band formed 2010 in the town of Sundsvall who have released two albums, Decomposed (2012 on Blood Harvest records) & Devouring (2014 on Memento Mori); and one demo, Stench Of Death (2011). Find them on facebook here: https://www.facebook.com/pages/Decomposed/184061241645341
3) A brutal death metal band from Indonesia, formed in 2001. They have released three EPs, a demo, and one split. They are currently active.
4) A death metal band from Philadelphia, Pennsylvania, USA formed in 1999 and released one album 'Torn From The Womb' on Worldeater records in 2006. Likely broken up.
5) A death metal band from France formed in 1989 and released one demo in 1991. Changed name to Occult and released a split and an EP, then broke up.
6) A death metal band from Czech Republic formed in 1993, released three demos and two splits. Broke up in 1999. An attempt to revive the band was made in 2005 but by 2010 it was hopeless.
7) A death metal band from Barcelona, Spain who released one demo in 1990. Changed name to Rotten Flesh in 1991, and changed name again to Undivine in 1993. Broke up shortly after.
8) A death metal band from Greece formed in 2002 and released one demo 'Unknown Creation' in 2004. Broke up.
9) A death metal band from California, USA who were featured on a split called 'The Heralds of Oblivion, vol 1' released in 1993. Released nothing more.
10) A thrash metal band from Corpus Christi, Texas, USA formed in 1987. Released one demo in 1988 then split up.
11) A death metal band from Monsey, New York, USA formed in 1990 and released two demos then split up.
12) A death metal band from Dallas, Texas USA who released a demo in 1991. Split up.
13) A death metal band from Nis, Serbia. No information is known about this band.