Mr Beshira, 21, was pronounced dead on Kilburn High Road in north-west London at 17:20 GMT on Thursday after being shot in the abdomen.
A 22-year-old man was arrested on Saturday on suspicion of murder and remains in custody.
Metropolitan Police said they believe Mr Beshira was shot on Palmerston Road and staggered 200 yards.
Officers are searching for a man described as slim and white who was wearing jeans and a dark top with his hood up and the lower half of his face covered.
Members of the public were already attending to Mr Beshira, who had collapsed outside a cafe, when the emergency services arrived.
Witnesses described the area as "mayhem" after the shooting with reports of fights breaking out in a crowd.
Det Ch Insp Andy Partridge said the gunman was "loitering in and around Palmerston Road and the Webheath Estate prior to the attack".
He said: "We know the area was extremely busy at the time of the shooting.
"I am convinced that other members of the public have either seen the incident itself, or have seen the suspect arrive at the scene or flee after the shooting."

The officer, 52, was seriously injured when a booby-trap device exploded under his van on Friday, 4 March.
Christopher Alphonsos Robinson, of Aspen Park in Dunmurry, County Antrim, appeared at Belfast Magistrates' Court.
The 45-year-old was also charged with possessing an improvised explosive device with intent to endanger life.
There was an increased police presence in court for the hearing.  A detective constable said he could connect Mr Robinson to the charges.
When asked by the clerk if he understood the charges, Mr Robinson did not reply, but let out a loud sigh.
A defence solicitor told the court that Mr Robinson was not applying for bail, but said during 16 police interviews, "no evidence was actually put" to the defendant to link him to the attack.
Mr Robinson was remanded in custody to appear again on 1 April via video-link.
A dissident republican group known as the New IRA has said it carried out the attack.

Audel, 30, ended a two-year association with the Magpies at the end of last season having made 53 appearances in all competitions.
The French centre-half has also played for Triestina and Pisa in Italy as well as Macclesfield, Crewe and Lincoln.
He is the National League Bluebirds ninth signing of the summer.
Find all the latest football transfers on our dedicated page.
Detectives have identified a man who was shot and killed on a busy street as Yasir Beshira.
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A man has appeared in court charged with the attempted murder of a prison officer in a bomb attack in Belfast last week.
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Barrow have signed defender Thierry Audel on a one-year deal with an optional second year, following his release by Notts County.