The student accused of stabbing four people at University of California was said to be carrying a printout of an Islamic State flag during the attack last week.

It was found among Faisal Mohammad's belongings, which also included a handwritten two-page note, a police source told the Merced Sun Star, which reported that the significance of those items was still being investigated.

Mohammad was shot and killed by a campus police officer after stabbing two students, a construction worker and a university employee.

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Stabbing: The 18-year-old freshman Faisal Mohammad, of Santa Clara, left behind a two-page ‘manifesto’ explaining that he was angry with being kicked out of a study group and a detailed plan of revenge

His family released a statement expressing their sympathy for the victims.

In their first comments since last week's attack, the family of Faisal Mohammad, described the freshman from Santa Clara, California, as a ‘kind and respectful young man’.

‘He was always quiet and humble and excelled in school and academics. His teachers and friends always spoke well of him,’ said the statement released through San Jose attorney Daniel Mayfield.

Authorities have said that Mohammad had no previous run-ins with police and no clues in his past behavior to indicate that he would try to kill his classmates as revenge for being kicked out of a study group.

Probe: Merced County sheriff Vern Warnke said that Mohammad wanted to do more harm but 'had little capacity to carry it out'

All the victims are expected to recover.

Merced County sheriff Vern Warnke said Mohammed left behind a two-page ‘manifesto’ explaining that he was angry with being kicked out of a study group and a detailed plan of revenge.

His teachers and friends always spoke well of him. Faisal Mohammad's family statement

Mohammad stabbed two students, a university employee and a construction contractor credited with interrupting the attack before campus police shot him to death.

According to the manifesto, Mohammad planned to bind students to their desks with zip-tie handcuffs.

Then, he was going to make a fake emergency distress call, ambush responding officers with the hunting knife he carried and steal their guns to shoot a list of targeted classmates, including those in his study group.

Mr Warnke called the plan the delusions of an angry young man, saying Mohammad wanted to do more harm but had little capacity to carry it out.

Background checks with help from the FBI and Department of Homeland Security showed no connections to organized hate or terror groups.

Saved: Police credit construction worker Byron Price (left) as saving the life of the first stabbing victim. He was stabbed by the student as he tried to intervene

Mr Warnke and school officials said that campus police would take over the investigation with assistance from the FBI.

Despite the sheriff's assurances, the Simon Wiesenthal Center, a Jewish rights organization based in Los Angeles, has called on federal officials to continue investigating Mohammad's background and activities for possible links to the Islamic State or other groups.

‘Clearly, an 18-year-old freshman would not know how to plan a major assault without having access to some form of training,’ said Rabbi Abraham Cooper, who heads the center's Digital Terrorism and Hate project.