Short answers, pulled from the story.
The inner German border ran 1,381 kilometres in an irregular L-shaped line from Dassow at the Baltic Sea to Eichigt at the border with Czechoslovakia. It existed from 1949 to 1990, when it was formally abandoned on the 1st of July 1990.
As of 2009, unofficial estimates put the death toll at up to 1,100 people over the border's 45-year existence. A further 189 people are estimated to have died attempting to flee via the Baltic Sea. The GDR treated exact figures as a closely guarded secret.
Freikauf was a semi-secret program in which the West German government paid to ransom political prisoners from East German jails. Between 1964 and 1989-33,755 political prisoners were freed. West Germany paid over 3.4 billion Deutsche Marks, equivalent to nearly 2.3 billion US dollars at 1990 prices, in goods and hard currency.
The fortifications were built to stop Republikflucht, the mass emigration of East German citizens to the West. Between 1949 and the construction of the Berlin Wall in 1961, an estimated 3.5 million East Germans, roughly a sixth of the population, emigrated. The GDR feared this exodus would destroy its economy.
On the evening of the 9th of November 1989, Politburo member Gunter Schabowski mistakenly announced at a press conference that the border would open immediately. Guards, unable to reach superiors for instructions, opened the gates. Within the first four days after the announcement, 4.3 million East Germans crossed into the West.
The SM-70 was a directional anti-personnel mine fitted to the outer fence of the inner German border from 1970. Around 60,000 were installed in total. Triggered by tripwires, each detonated a horn-shaped charge that sprayed shrapnel up to 20 metres. The GDR removed them by the end of 1984 following international condemnation.