**US President Barack Obama is due to attend a memorial service in Texas for the 13 people who died in a shooting at an army base last week.**Mr Obama will first meet privately with the families of those killed, as well as some of the 29 people injured.
Maj Nidal Malik Hasan, who is suspected of being behind the Fort Hood massacre, was shot and remains in hospital.
US intelligence authorities have said they knew Maj Hasan had been in contact with a cleric sympathetic to al-Qaeda.
An FBI-led task force monitoring the e-mail of Yemen-based Anwar al-Awlaki said he had communicated with Maj Hasan - a US-born Muslim and army psychiatrist - on 10 to 20 occasions.
However, it was decided that further investigation was not needed, as the content of the messages did not advocate or threaten violence.
“This murderous attack should be examined from every angle to make sure nothing like this occurs again”
Senator Joe Lieberman
Meanwhile, the Senate Homeland Security Committee has confirmed it will hold an inquiry into the shootings.
On Monday, Mr Obama said he wanted to visit Fort Hood, the largest US military base in the world, “to personally express the incredible heartbreak that we all feel for the loss of these young men and women”.
He told ABC News that the authorities would “take whatever steps are necessary to make sure that something like this doesn’t happen again”.
Several other senior US officials will also attend the ceremony at Fort Hood, including Defence Secretary Robert Gates and Texas Governor Rick Perry.
‘Warning signs’
Maj Hasan is recovering from gunshot wounds at a military hospital and will be charged in a military court over the Fort Hood shootings - he has declined to be interviewed by investigators.
His motives remain unknown. Some reports have indicated he was unhappy about his imminent deployment to Afghanistan.
On Tuesday, the Senate Homeland Security Committee announced it would hold a full investigation into the attacks, starting with a public hearing next week.
Senator Joe Lieberman, who chairs the committee, said the “murderous attack should be examined from every angle to make sure nothing like this occurs again”.
He said investigators would seek to determine Maj Hasan’s motives and “whether the government missed warning signs that should have led to expulsion, and what lessons we can learn to prevent such future attacks”.
Mr Lieberman said the authorities would “do no favour” to Muslims serving in the US army by “ignoring real evidence” that Maj Hasan may have held violent extremist views.
FBI Director Robert Mueller has ordered a review of how the agency dealt with information about Maj Hasan.
A senior Republican on the House of Representatives Intelligence Committee has called on all the US intelligence agencies to preserve the information they have on Maj Hasan.