Police from Colombia and Paraguay are working with agents from the US Drug Enforcement Administration (DEA) and the FBI to hunt down the killers of an anti-mafia prosecutor.
Paraguayan prosecutor Marcelo Pecci, 45, was shot dead on Tuesday on a beach in Colombia, where he was on honeymoon.
Pecci investigated high-profile corruption and money-laundering cases in his native Paraguay.
His murder was likely related to his fight against crime, police say.
Pecci and his wife were on the sixth and final day of their honeymoon in Colombia when he was killed on Baru, an idyllic island off the Caribbean coast.
Just two hours earlier, his wife, journalist Claudia Aguilera, had posted a picture on her Instagram account announcing that they were expecting a baby.
She said that they were on a stretch of private beach of Decameron Hotel on Tuesday morning when her husband was targeted.
"Two men attacked Marcelo. They came in a small boat, or on a jet ski, the truth is I did not see well," she told El Tiempo newspaper.
She said that one of the men got off and "without a word he shot Marcelo twice, one [bullet] hit him in the face and another in the back".
Colombian police have released a blurry photo and a sketch of a suspect and announced a $500,000 (£410,000) reward for information leading to an arrest.
Police Chief Jorge Vargas said that US and Paraguayan investigators would help Colombian security forces hunt down the killers and those who may have ordered the assassination.
Gen Vargas said that the "big hypothesis" was that the murder was related to some of the high-profile cases Pecci had been involved in Paraguay.
Pecci was part of "A Ultranza Py", the biggest operation against cocaine trafficking and money laundering in Paraguay's history.
According to Paraguayan media, the operation broke up a ring which smuggled drugs from cocaine-producing hotspots Colombia and Bolivia through Paraguay to Europe.
Pecci was part of the international team which earlier this year seized hundreds of millions of dollars in assets and arrested dozens of suspects.
The US Bureau of International Narcotics and Law Enforcement Affairs said that "Pecci's work fighting organised crime stands as an example to us all - especially his efforts to bring to justice those who engaged in money laundering, drug trafficking, and corruption".
While Pecci had bodyguards in Paraguay, he did not have any protection while on his honeymoon in Colombia and the Colombian police said it had not been aware of his presence in the country.
His wife said that he had not received any threats although a friend of Pecci's has since told Paraguayan media of a suspicious incident on his wedding day.
Sebastian Achá told ABC newspaper that a SUV without number plates had tried to block Pecci's car on his way back from the ceremony on 30 April, an attempt which was thwarted by Pecci's bodyguard, who was driving at the time.