Dorchester County investigators smelled the tang of marijuana in the air soon after they hopped the gate of a former state trooper's rural Ridgeville property in January 2010.

The weed's smell drifted from a portable container near a shed where a sheriff's deputy heard the hum of indoor lights. Hoses snaked from the container to a nearby pond. Electrical wires ran between the shed and a smaller out-building.

These observations helped deputies uncover what prosecutors describe as an elaborate and illicit indoor growing operation.

But the question is: Should investigators have been there in the first place?

The attorney for former Highway Patrolman Kurt Steffen wants a judge to consider tossing out the evidence against him, alleging that it resulted from investigators trespassing on his property without a warrant, in violation of Steffen's constitutional rights.

A hearing on that motion, filed by Public Defender Mary Gordon Baker, is scheduled for Thursday in U.S. District Court in Charleston.

A ruling in Steffen's favor could hurt the government's efforts to tie the

30-year-old former trooper to some 315 pot plants seized on his land. Authorities say Steffen, who resigned from the Highway Patrol in December 2009, was part of a ring that conspired to distribute at least 1,000 pot plants in the Charleston area.

Federal prosecutors maintain the defense motion to suppress evidence is full of smoke. They insist deputies acted prudently and with the blessing of local prosecutors as they worked within the law to build a case to search the property.

They also point out that a state judge already upheld the search in a case involving one of Steffen's co-defendants, according to court documents.

Dorchester County sheriff's Maj. John Garrison said deputies did nothing wrong.

"I think we acted in good faith and acted on good advice," he said. "So we are going to stand by it."

First Circuit Solicitor David Pascoe, whose office advised deputies on the warrantless January 2010 visit, concurred.

"I commend law enforcement for how they conducted the investigation," he said.

Dorchester deputies got their first whiff of trouble at 300 Stable Lane in November 2009 when Edisto Electric notified them of extraordinarily high electricity use on the property. Steffen and his wife owned the land and rented it to others, court documents state.

A deputy went to the 5-acre, fenced tract and spotted a portable storage container, large bags of potting soil and a shed emitting a humming sound from indoor lights. Baker argues that the deputy trespassed on Steffen's property to make that find, but prosecutors insist he was on neighboring land.

After surveillance on the property failed to spot people or vehicles on the land, investigators met with local prosecutors to discuss the possibility of conducting a warrantless search. Prosecutors gave them the go-ahead as long they didn't enter any buildings, based on a legal doctrine that permits warrantless searches of open fields, court documents show.

A search on Jan. 5, 2010, helped deputies compile the probable cause needed to gain a search warrant. They returned to the property that day and found 105 marijuana plants in a sport utility vehicle and 210 more in the structures, along with thousands of dollars worth of growing equipment, prosecutors said.

Baker did not return a phone call Monday. But in court papers, she argues that it's unclear whether the property qualifies as an open field and that the first deputy's visit was "based on the thinnest of reasoning, a high electric bill."

Baker states a hearing is needed to determine whether deputies violated Steffen's constitutional protections against unreasonable searches.

In their response to her motion, federal prosecutors argue that the property is clearly an open field and that deputies followed the letter of the law in conducting their visits.

Reach Glenn Smith at 937-5556 or Twitter.com/glennsmith5.