Germany has arrested two of its citizens and charged them with helping Iran obtain German technology needed to build nuclear warheads for ballistic missiles. A Russian and a North Korean were also accused of helping the Germans. While little discussed in the media, the warhead for a nuclear missile is one of the more difficult bits of technology to develop. A nuclear weapon is a precision machine, containing many complex electronic, mechanical and chemical components. The ballistic missile basically carries the warhead outside the earth's atmosphere, and then sends it back ("reentry") at speeds in excess of 20,000 kilometers an hour (nearly six kilometers a second). It's this speed that creates tremendous heat, as the warhead enters the atmosphere. The high speeds also create high G forces and vibration. All this generates some very unfriendly conditions for the components of the nuclear device. It is not easy to build a warhead that can keep the nuclear device in operating order. The two Germans were specifically charged with getting a vibration testing device out of the country, and to Iran. This device makes it possible to test nuclear bomb and warhead structure components without having to launch a missile.
The Russian connection is ominous, because Russia has lots of proven warhead technology. North Korea is also working on designing warheads for nuclear weapons. Iran has long used bribed foreigners to help them get military technology and equipment for them, stuff that no nation would knowingly sell to Iran.