German investigators are examining the background of a Moroccan student arrested over the Madrid bombings, after it emerged he lived in Germany.
Some of the bombing suspects have appeared in court
The man's flat has been searched but prosecutors say they have no evidence the attacks were planned in Germany.
The 28-year-old is among 19 people being held in connection with the train attacks earlier this month.
Meanwhile, Morocco says it has arrested several people over the Madrid blasts, which left 190 people dead.
However, a government spokesman denied a report that a man had been arrested in Tetouan, 280 kilometres (175 miles) north of the capital, Rabat, with maps of the Madrid train stations hit by the bombs.
In Madrid, another suspect was arrested on Friday evening, but no further details were released.
Meanwhile, two Moroccan suspects detained in previous waves of arrests went before the National Court on Friday.
Another five, arrested on Wednesday and Thursday, will be questioned on Monday at the national court, sources told the Associated Press news agency.
German police searched the flat in the western city of Darmstadt in connection with the bombings after news that one of the suspects arrested in Spain had lived in Germany.
Prosecutors said they were investigating the 28-year-old on suspicion of belonging to a foreign terrorist organisation and other crimes.
The man had registered in Darmstadt in October 2003, but it appears he only stayed a few days in the country.
Spanish police have 18 people in custody over the attacks
The BBC's Ray Furlong said a German link to the Madrid bombings would be especially sensitive, as three of the 11 September 2001 hijackers were based in Hamburg.
The daily Die Welt newspaper said he had been earmarked by German authorities as a "dangerous" Islamist figure who was ready to use violence.
Other media reported that as many as three suspects being held in Spain may have lived in Germany.
In the United States, the Director of the Central Intelligence Agency (CIA) George Tenet said intelligence "strongly" suggested extremists linked to al-Qaeda were responsible for the Madrid bombings but there was no information that the leadership of Osama Bin Laden's network ordered the attack.