G.I. Joe: Retaliation

Duke (Channing Tatum) has become the leader of the G.I. Joe unit, which is framed for stealing nuclear warheads from Pakistan by Zartan (Arnold Vosloo), who is impersonating the President of the United States (Jonathan Pryce). The unit is subsequently decimated in a military air strike with Duke among the casualties. The only survivors are Roadblock (Dwayne Johnson), Flint (D.J. Cotrona), and Lady Jaye (Adrianne Palicki).
Meanwhile, Storm Shadow (Byung-hun Lee) and Firefly (Ray Stevenson) rescue Cobra Commander (Luke Bracey) from an underground maximum-security prison in Germany, leaving Destro behind. Storm Shadow is injured during the escape and retreats to a temple in the Himalayas to recover. Upon learning that he is alive, the Blind Master (RZA), leader of the Arashikage Clan, sends Snake Eyes (Ray Park) and his apprentice Jinx (Ãlodie Yung), Storm Shadow's cousin, to capture Storm Shadow so he can answer for the murder of his uncle, the Hard Master.
Roadblock, Flint, and Lady Jaye return to the United States where they set up a base of operations in a rundown gym. After Zartan announces that Cobra will replace the Joes as America's elite special forces unit, Lady Jaye deduces that someone is impersonating the President, and Roadblock leads them to General Joseph Colton (Bruce Willis), who provides them with weapons, and helps them infiltrate a fundraising event that the President will be attending. Lady Jaye steals a sample of the President's DNA and confirms that he is Zartan. They escape after a confrontation with Firefly and Zandar (Matt Gerald), the head of the U.S. Secret Service's Presidential Detail and a member of Cobra.
Snake Eyes and Jinx locate and capture Storm Shadow after a battle with ninjas and take him to Japan, where Storm Shadow reveals that Zartan murdered the Hard Master, and that he joined Cobra to avenge his uncle. Storm Shadow then accompanies Snake Eyes and Jinx as they join the Joes' efforts to stop Cobra.
Zartan invites the world leaders to a summit at historic Fort Sumter, where he blackmails them into disabling their nuclear arsenals, and reveals that he has created Project Zeus: seven orbital kinetic bombardment weapons of mass destruction at his command. He destroys Central London to prove his superiority, and threatens to destroy other capitals if the countries don't submit to Cobra. Storm Shadow betrays Cobra Commander and kills Zartan, revealing Cobra's deception to the world leaders. While Snake Eyes, Jinx, and Flint fight Cobra's soldiers, Cobra Commander activates the remaining six weapons and instructs Firefly to protect the launch device. Firefly is killed in combat by Roadblock, who deactivates and destroys the orbital weapons. Meanwhile, Colton and Lady Jaye rescue the President.
Cobra Commander escapes during the battle and Storm Shadow disappears after avenging his uncle. The real President addresses the nation at a White House ceremony where Roadblock, Lady Jaye, Flint, Jinx, and Snake Eyes are commemorated as heroes. Colton presents Roadblock with an M1911 pistol that belonged to General George S. Patton, to use when he finally finds Cobra Commander and to avenge Duke. Roadblock proudly raises the weapon and fires a single shot in honor of his fallen comrades.

Question: who murdered the Hard Master?
Answer: Zartan; Zartan