"There was a great interest," said Clas Svahn at UFO Sweden.
A Swedish pilot in a Draken plane was flying over Småland in a training exercise in the 1970s. He received the order to break the exercise and fly towards an unidentified object lying still on the water.
As he approached the object suddenly shoots straight up - and the pilot takes up the chase. Despite full speed the pilot soon loses the object and it is never identified.
The event which confounded the pilot, is just one of the reports recorded in the world's largest UFO archive in Norrköping in eastern Sweden. It is one of up to 1,000 reports worth taking a closer look at, according to Clas Svahn.
The Swedish UFO association held a series of lectures on Saturday in connection with the temporary opening of the archive.
"175 came to listen and there was a great interest. There were more than we have seen in recent years and there was a serious interest. We are very happy," he said.
There were then around 70 people in Norrköping for the opening of the archive on Sunday.
The archive is now closed once more, as the association works on a voluntary basis and does not have the time to do more than show the archive to, for example, researchers.
"One can come and have a look but in that case you have to arrange an appointment."
In response to the question over whether he believes in the existence of UFOs, Svahn answered:
"I am completely convinced that there is life in space. If life can exist here then it can exist elsewhere. But can they travel here? There is no conclusive evidence, but I do not want to answer for certain. There are mysterious phenomena that we can not identify, and they are not only optical illusions," Clas Svahn said.