Spanish authorities who raided what is thought to be the country's largest outdoor marijuana planation didn't have far to look for the prime suspect. He was in jail.

The 47-year-old Spaniard arranged for others to cultivate a three-hectare (7.4 acre) olive grove he had purchased while on prison leave, Interior Ministry spokesman Federico Pozuelo said Saturday.

The prisoner relied on a 59-year-old Lithuanian assistant and a staff of five to tend 75,000 cannabis plants, which weighed five metric tons and were valued at 5 million euros ($5.6 million), police said.

Special plants that only grow to a height of 40 centimeters (15.7 inches) and look more like ordinary weeds than normally tall marijuana bushes were sown between rows of well-established olive trees and watered by a sophisticated drip-irrigation system, police said.

The arrests were made when the plantation was raided just as crop harvesting had begun and 5,000 plants were drying in a building containing a clandestine laboratory and packing facility.

Police said the farm in the central Albacete region was surrounded by a protective perimeter wall of dung and garbage that masked the plants' telltale aroma.

Two Spaniards, three Moroccans and the Lithuanian were arrested, Pozuelo said. One suspect was armed with a loaded handgun at the time of the arrests, police said.