Delegates to a three-day Latin American clown convention in Mexico City have distanced themselves from the murder last week of a drug lord by a hitman in fancy dress, insisting no genuine member of their profession would have committed the crime.

Convicted drug trafficker Francisco Rafael Arellano Felix was shot dead on Friday in the Baja beach resort of Los Cabos by a gunman wearing a clown costume, complete with wig and a rubber nose. The dead man was the eldest brother of Mexico's once-feared Arellano Felix clan.

Clowns queue to register for the convention. Photograph: Dario Lopez-Mills/AP

Clown leader Tomas Morales, a 21-year veteran of the trade who goes by the stage name Payaso Llantom, said he was certain the killer was not a professional clown. He said clowns in Mexico, especially in outlying states, know each other, and their costumes and makeup are individualised and recognisable.

"The people who do that, they're not clowns. I can swear on my mother's grave it wasn't a clown," said Morales, whose costume includes frizzy blue hair and a tiny top hat. "We are not like that … we are non-violent."

Bufon Marley, the stage name of 49-year-old Alberto Villanueva who dresses like a medieval jester, said of the killer: "It's sad that it has fallen to that level."

"I don't think it will hurt our profession, because in our communities, people know us."

A clown and his daughter wait for the start of a laugh-a-thon. Photograph: Dario Lopez-Mills/AP

Morales said, however, that there was a precedent of thieves stealing clown costumes to commit crimes.

"We clowns suffer robberies," Morales said. "The criminals have stolen our vehicles, our costumes, our sound equipment, our makeup, and with these same tools we use to work, they use them to commit robberies."

An estimated 500 clowns from around Latin America gathered on Wednesday at the International Clown Meeting in Mexico City and held a 15-minute laugh-a-thon to demonstrate their opposition to the violence that prevails in the country.

As hard as it might sound to be a clown in a country so riven by crime and violence, the laughing came naturally, Villanueva said.

"We laugh at the very things that hurt us," he said. "It is a very special, very Mexican humour."