The captain of a cargo ship arrested after the collision in the North Sea was kept in custody for another 24 hours “due to the complexity of the incident,” police said.
The 59-year-old Russian man has been arrested on suspicion of negligence and manslaughter.
US registered tanker Stena Immaculate, which carried 220,000 barrels of aviation fuel, and Portuguese-sized cargo ship Solong crashed from the East Yorkshire coast on Monday.
Humberside police said detectives will be given time to question the man after the magistrate previously granted the 36-hour extension on Wednesday.
Both ships were engulfed in flames, and 36 crew members were rescued.
It is estimated that Solon’s crew was missing and died.
In a statement, Humberside Police said: “Additional time was essential for the investigation, as we established the complexity of the incident with sea vessels, the number of witnesses involved, and the scene to collate and collect information and evidence.
“A large-scale research line is continuing and further updates are provided as much as possible.”
Officials said they continue to support the families of missing crew members “who were believed to have died.”
The force is conducting an investigation in parallel with the Marine Accident Investigation Division (MAIB), which is trying to establish the cause of the crash.
On Friday, Chief Coast Guard Paddy O’Callaghan said “only a ‘small cyclic pocket’ of solo.”
He added that regular airborne monitoring flights continued to monitor the containers, confirming that neither vessel had “no cause of any contamination concerns.”
In his initial enquiries, Maib said he discovered Solon was traveling from Grangemouth to Rotterdam and was often sailing the same route.
“At 09:47 gmt, I collided with the Immaculate Confession of Stena, who was anchored from the entrance to the Humber River,” Maib said.
The ship was travelling at approximately 16.4 knots (18.9 mph).
The agency added that it will gather witness accounts and examine the navigation practices of both vessels, manning and fatigue management, the state and maintenance of the vessels involved, and environmental conditions at the time.
The BBC understands that all 23 crew members on the Stenna Immaculate are Americans currently in Grimsby and are likely to have been repatriated in time.
Maibu said Portugal and the United States are leading a safety investigation into the incident as they function as “substantially of interest.”
